Current ATM communications systems may transport communications traffic over switched virtual circuits (SVC) or permanent virtual circuits (PVCs). SVCs are set-up and torn down as requested--like telephone calls. PVCs are provisioned through an ATM network and are used like a dedicated communications channel. Aside from PVCs and SVCs, Permanent Virtual Paths (PVPs) and Switched Virtual Paths (SVPs) are also available. The use of SVCs or SVPs typically results in more efficient use of ATM bandwidth. As is known, ATM communications paths are logically designated by the Virtual Path Identifier (VPI) and the Virtual Channel Identifier (VCI) located in the ATM cell header.
ATM cross-connect devices route ATM traffic by associating virtual connections. A cross-connect associates two virtual connections by changing the VPI/VCI of ATM cells from one virtual connection to the VPI/VCI of the other virtual connection. For PVCs or PVPs, these routes have been pre-provisioned. This means that the routing configuration is set and remains static. Typically, a cross-connect has multiple routing configurations that are stored in memory. Network administration can select different routing configurations, but changes are not implemented dynamically on a call-by-call basis. In any event, the number of routing configurations required to support call routing would be prohibitively complex. In a provisioned cross-connect, the VPI/VCIs in incoming cells are changed to pre-assigned VPI/VCIs.
SVCs and SVPs are handled differently. Since the VPI/VCIs are set-up and torn down frequently, provisioned routing configurations with pre-assignments of VPI/VCIs are not possible. For SVCs and SVPs, the VPI/VCIs are dynamically selected in real time on a call-by-call basis by an ATM switching function. The switching function makes the selections by processing of information in telecommunications signaling. An example of such signaling is B-ISUP signaling.
Some ATM systems use pre-provisioned PVPs to connect the network elements, and then dynamically select SVCs within the PVPs. In this way, network elements can each be interconnected by PVPs to form a flat architecture, and SVCs can be dynamically allocated to maximize efficient use of bandwidth. In this environment, problems are caused when one network is connected to another network. Current signaling capability required by the switching function is not able to handle high volumes of traffic. This impairs the ability of separate networks to dynamically allocate SVCs between multiple cross-connects on a call-by-call basis. As for the PVPs, extensive administrative information must be shared to coordinate all of the PVP provisioning between the two networks. An additional coordination problem occurs with signaling between networks. When networks interface at multiple points, signaling routes must be defined so each interface point can signal the opposing interface points.
One solution is to install complex ATM switches with full signaling capability. At present, such devices are not readily available at the quality and cost required for a robust and cost-effective deployment. There is a need for a cost-efficient system to interface between two ATM networks and alleviate the problems described above--namely the coordination of PVPs and SVCs.
Gateways are devices that interface different networks or systems. They allow interconnection between different networks that are not coordinated. Some examples are Internet Protocol (IP) bridges and X.75 gateways. But, these systems are not able to interface PVPs and SVCs of two ATM networks. These devices are not capable to handle ATM. Additionally, they are not designed to handle the dynamic allocation of connections required for SVCs. Thus, an ATM gateway is needed to interface two ATM networks. This ATM gateway must be able to handle the dynamic allocation of VPI/VCI connection assignments required to support SVCs.